Known is a method of fabricating a semiconductor device by connecting the electrodes of a semiconductor chip to the leads connected to the external terminals by wire bonding, this method is applied regardless of package form. Also known is a method of fabricating a semiconductor device by use of a lead frame. The following outlines this later method.
As is well known, a semiconductor chip formed with an integrated circuit is mounted on the island of a lead frame with an adhesive, for example. Plural electrode pads on the semiconductor chip are connected to corresponding leads with metal fine wires (or wire). Then, the semiconductor chip and the surroundings thereof are integrally molded for resin encapsulation with a resin such as a synthetic resin. The leads of the outer side of resultant resin-molded package are ultimately separated from the lead frame, and appropriately bent and cut, if necessary. Thus, a semiconductor device can be fabricated.
To attach the metal line wires bonds between the plural electrode pads on the semiconductor chip mounted on the island and the surface of the corresponding leads, a metal line wiring apparatus known as a wire bonder must be programmed to recognize the electrode pads and the corresponding leads. To do so, the edge of each lead must be captured as an optical image to store the contour of the lead in the memory of the wire bonder.
In recognizing the leads of a semiconductor device lead frame, the wire bonder makes use of the external view of each lead as a reference. Therefore, a lead having a defect such as torsion, luster, or rough surface causes a wide variation in the recognition accuracy of the wire bonder.
Recently, the increasing number of pins on one semiconductor device inevitably increases the number of leads thereof and the miniaturization of semiconductor devices accordingly decreases the width of each lead and the interval between leads (or the lead pitch). Currently, a typical lead width is as small as 0.07 mm and a typical lead pitch is 0.16 mm. Consequently, as the lead width and the lead pitch narrow, it is more difficult, when connecting the plural electrode pads arranged on a semiconductor chip to the corresponding leads with metal line wires, for the metal line wire to be connected to the lead at the center along the width of the lead.
Such being the case, attaching the metal line wire to the lead off-center of the width or, detachment of the metal line wire from the lead causes a connection failure. Therefore, no matter how small the lead gets, the center of each lead is must be accurately recognized. Conventionally, however, if the lead has inadequate flatness or distortion, the center of each lead cannot be optically recognized with a high degree of precision.
It is therefore an object of the present invention to provide a semiconductor substrate, a lead frame, a semiconductor device, a method of fabricating the same, a circuit board, and an electronic apparatus that facilitate the optical recognition to prevent poor wire bonding.